Jonathan Bain (New York University)
Naturalness, as a guiding principle for effective field theories (EFTs), requires that there be no sensitive correlations between phenomena at low- and high-energy scales. This essay considers three reasons to adopt this principle. The first two are that it has been empirically successful, and that it is consistent with what Williams (2015) calls a "central dogma" of EFTs; namely, that phenomena at widely separated scales should decouple. I argue that these are not compelling reasons: The modest empirical success of naturalness must be balanced by spectacular empirical failures, and a distinction between two types of EFTs, Wilsonian and continuum, suggests that while decoupling may be a central dogma of EFTs, naturalness is not. On the other hand, a third reason to be natural is that it underwrites a non-trivial notion of emergence. Thus to the extent that one desires to interpret EFTs as describing emergent phenomena, one should be natural.
